Date issue

I have a date field that has the following formats for dates.
9/1/2009
10/27/09
09/10/2009
I want to covert them all to mm/dd/yyyy format.
I used the followig code:
sh_date1=input(ship_date,anydtdte10.);
format sh_date1 mmddyy10.;
sh_date2=put(sh_date1,mmddyy10.);
drop ship_date sh_date1;
rename sh_date2=ship_date;

The dates that are in the format 09/10/2009 are shown as blank.
How to avoid this?